Field of the Invention
The present invention relates generally to snow plows for use with light and medium duty trucks, and more particularly to an improved snow plow blade having a fixed upper plow blade and a pivoting lower trip blade mounted on the swing frame of the snow plow with the axis of rotation of the trip blade being directly in line with the swing frame and the support frame of the snow plow.
Once the exclusive domain of municipality-operated heavy trucks, snow plows have been used with light and medium duty trucks for decades. As would be expected in any area of technology which has been developed for that period of time, snow plows for light and medium duty trucks have undergone tremendous improvement in a wide variety of ways over time, evolving to increase both the usefulness of the snow plows as well as to enhance the ease of using them. The business of manufacturing snow plows for light and medium duty trucks has been highly competitive, with manufacturers of competing snow plows differentiating themselves based on the features and enhanced technology that they design into their products.
When plowing snow, a not infrequent occurrence is striking an object which is concealed beneath the snow. This occurs particularly often when plowing roads which are not paved, such as, for example, gravel roads or dirt roads. Since roads being plowed are typically frozen, it is common for an object of significant size to become frozen into the road. For example, medium size rocks or sticks which would not present a significant obstacle were they loose on the surface of the road can present a problem when they are frozen into the surface of the road and concealed beneath a layer of snow. In addition, when significant snow depth covers the area being plowed, the operator may miscalculate and drive the snow plow into a fixed obstacle such as a curb.
For this reason, snow plow blades have been manufactured for some time with a blade trip mechanism which allows the bottom of the blade to yield upon substantial impact. This is accomplished in one of two different types of implementation: 1. the snow plow blade is mounted on its support structure using a pivoting mechanism where the entire snow plow blade pivots when the bottom of the snow plow blade encounters an obstacle; or 2. a trip blade is hingedly mounted at the bottom of an upper blade and pivots when it encounters an obstacle. In the first type of mechanism, the snow plow blade is mounted onto the support structure at a position between eight and sixteen inches above the ground in a manner which permits the bottom of the snow plow blade to pivot back when an object is struck. Simultaneously as the bottom of the snow plow blade pivots back, the top of the snow plow blade will pivot forward.
This movement between the normal plowing position of the snow plow blade to the position in which the bottom of the snow plow blade pivots fully backward is referred to as blade tripping. The movement of the snow plow blade from the normal plowing position to the tripped position is resisted by two or more strong trip springs which are mounted behind the snow plow blade, typically running from positions near the top of the snow plow blade to the snow plow blade support structure. Even when the snow plow blade is in its normal plowing position, the trip springs are under tension. Accordingly, it will be appreciated that when the bottom of the snow plow blade is forced backward, the trip springs will provide a strong resistance to the movement, tending to absorb some of the force of the impact of the snow plow blade with the object which has been struck.
In a typical embodiment, the snow plow blade is supported at two pivot points on the right and left sides of the snow plow blade by a swing frame. The snow plow blade has a plurality of vertically extending curved ribs which are connected between top and bottom plow frame members, and two of these ribs have apertures located between approximately eight and sixteen inches from the bottom of the snow plow blade. The snow plow blade is pivotally mounted to the swing frame using these apertures. The trip springs are mounted between the snow plow blade and the swing frame to provide the tripping resistance force.
The trip springs are mounted to the snow plow blade using apertures located either in the ribs or in the top frame member, or using brackets mounted onto one or more of these members. The trip springs may be mounted at one end to the top frame member and the ribs from which the snow plow blade is pivotally supported. The other ends of each of the trip springs are mounted to the snow plow blade support structure, typically using brackets which may be mounted, for example, on the swing frame. The points of connection of the trip springs on the swing frame or other snow plow blade support structure are typically located closer to the center of the snow plow than is the point of connection of the trip springs to the snow plow blade.
Although the predominant force exerted by the trip springs on the snow plow blade is orthogonal to the axis on which the snow plow blade pivots, a significant portion of the force is exerted in a lateral direction which is parallel to that axis. This component of the spring force is detrimental to the structural integrity of the snow plow blade frame, which is not constructed to resist forces in a lateral direction. Although the trip springs are located on both sides of the snow plow blade, and the lateral forces exerted by them thus tend to offset, over time their presence can cause blade distortion or other damage. In addition, it will be appreciated by those skilled in the art that since not all of the force exerted by the trip springs is in the direction orthogonal to the axis on which the snow plow blade pivots, the trip springs must be larger in order to provide the desired force in this orthogonal direction than they would otherwise be if all of the force which they exerted were in this orthogonal direction.
An improved version of the first type of blade tripping mechanism in which the entire blade pivots is illustrated in U.S. Pat. No. 6,701,646, to Schultz et al., which is assigned to the assignee of the present invention. This patent discloses an improved snow plow which has blade trip springs which are mounted using brackets located to direct the force of the springs in directions which are orthogonal to the axis upon which the plow blade pivots, thereby increasing the predictability of the tripping forces exerted by the trip springs as well as eliminating lateral trip spring forces which could warp the plow blade. The forces exerted by the trip springs are exerted proximate planes which are orthogonal to the pivot points at which the snow plow blade is mounted to the snow plow blade support structure. Either a single trip spring on either side of the snow plow blade or two trip springs on each side of the snow plow blade are used, with the size of the trip springs being minimized by ensuring that all of the forces which they exert are directed properly in the requisite directions. U.S. Pat. No. 6,701,646 is hereby incorporated herein by reference in its entirety.
In the second type of mechanism mentioned above, a trip blade is hingedly mounted at the bottom of an upper blade which is supported from the chassis of the plow, and when the trip blade encounters an obstacle, only the trip blade pivots. Examples of such trip edge snow plow blades are found in U.S. Pat. No. 5,191,729, to Verseef; U.S. Pat. No. 5,353,530, to Pieper; U.S. Pat. No. 5,437,113, to Jones; and U.S. Pat. No. 5,697,172, to Verseef. These presently known trip edge snow plow blades all possess several disadvantages, which will be discussed in the following paragraphs.
First, presently known trip edge snow plow blades all mount the top of the trip edge blade from the bottom of the upper blade. This subjects the upper blade to substantial forces which can cause blade distortion or other damage, or which alternately require substantially heavier construction, which in turn is disadvantageous both in terms of cost to purchase and operate, and also in terms of plow performance. In addition, many of the presently known trip edge designs have the hinge mechanism between the trip edge blade and the upper snow plow blade fully exposed at the front of the snow plow blade, where the hinge mechanism is highly susceptible to damage due to impact with obstacles.
Second, presently known trip edge snow plow blades have their axis of rotation located in a horizontal plane which is not aligned with the supporting frame of the snow plow, thereby causing rotational torque to be imparted to the supporting frame of the snow plow. Since most presently known trip edge snow plow blades have a trip edge blade which is five or six inches high (12.7 to 15.24 cm high), which means that the axis of rotation of the trip edge blade is below the level of the supporting frame of the snow plow, this rotational torque will add to the normal compressive forces present in the mechanical linkage between the supporting frame of the snow plow and the blade of the snow plow, causing additional stresses and wear. This undesirable situation is compounded by the fact that most presently known snow plows already have rotational torque due to the fact that the snow plow blade is mounted below the level of the supporting frame of the snow plow.
Third, presently known trip edge snow plow blades for the most part are highly susceptible to damage caused by hitting a snow-covered curb which is not visible to the driver of the truck on which the snow plow is mounted. This is due to the fact that most commercially-available snow plows have a short trip edge blade as mentioned above—typically only five or six inches high (12.7 to 15.24 cm high) when the snow plow is operated with a new wearstrip at the bottom edge of the trip edge blade. When this wearstrip wears down, the actual height of the trip edge blade will be even lower. Since most curbs are made at a standard height of six inches (15.24 cm), it will be at once appreciated by those skilled in the art that if a snow plow blade with such a short trip edge blade runs into a curb, the tripe edge blade will be tripped, but the bottom of the upper blade will also strike the curb, potentially causing significant damage to the snow plow blade.
It is accordingly the primary objective of the present invention that it provide a trip edge snow plow blade which is mounted onto the swing frame of the snow plow so that the swing frame, and thus the supporting frame of the snow plow, provides at least a substantial portion of the support for the trip edge snow plow blade. It is a related objective of the present invention that forces inherent in the tripping action of the trip edge snow plow blade be transmitted directly to the swing frame and the supporting frame of the snow plow rather than being transmitted to the upper snow plow blade. It is a further objective of the present invention that the hinge mechanism used to pivotally mount the trip edge snow plow blade is not exposed at the front of the snow plow blade where it would be susceptible to potential damage caused by objects struck by the snow plow.
It is another objective of the present invention that the axis of rotation of the trip edge snow plow blade be located at the height of the supporting frame of the snow plow in order to prevent the creation of torsional forces and to ensure that the load imparted to the supporting frame be substantially compressive in nature. It is still another objective of the present invention that the forces of the springs which bias the trip edge snow plow blade into an untripped position be carried by the swing frame of the snow plow rather than being exerted upon the upper snow blow blade. It is yet another objective of the present invention that the trip edge snow plow blade be substantially higher than the height of most previously known trip edge blades to prevent damage to the upper snow plow blade due to impacts with curbs or other high obstacles.
The trip edge snow plow blade of the present invention must also be of construction which is both durable and long lasting, and it should also require little or no maintenance to be provided by the user throughout its operating lifetime. In order to enhance the market appeal of the trip edge snow plow blade of the present invention, it should also be of relatively inexpensive construction to thereby afford it the broadest possible market. Finally, it is also an objective that all of the aforesaid advantages and objectives of the trip edge snow plow blade of the present invention be achieved without incurring any substantial relative disadvantage.